Method for continuous and controllable production of single walled carbon nanotubes

ABSTRACT

The present disclosure is directed to methods for producing a single-walled carbon nanotube in a chemical vapor deposition (CVD) reactor. The methods comprise contacting liquid catalyst droplets and a carbon source in the reactor, and forming a single walled carbon nanotube at the surface of the liquid catalyst droplets.

This application is a non-provisional application and claims priority toU.S. Provisional Patent Application Ser. No. 62/022,398 filed Jul. 9,2014 for “METHOD FOR CONTINUOUS AND CONTROLLABLE PRODUCTION OF SINGLEWALLED CARBON NANOTUBES”, which is hereby incorporated by reference intheir entirety.

BACKGROUND

The present disclosure relates to methods for producing a single-walledcarbon nanotube in a chemical vapor deposition (CVD) reactor comprisingcontacting liquid catalyst droplets and a carbon source in the reactor,and forming a single walled carbon nanotube at the surface of the liquidcatalyst droplets.

Single-walled carbon nanotubes (SWNT) are increasingly becoming ofinterest for various applications in nanotechnology because of theirunique electronic structures, which gives them exceptional thermal,mechanical, and electrical properties. For example, SWNT can be used inelectronics, energy devices, medicine, and composite materials in orderto obtain desirable physical and chemical properties. These uses requiremethods for producing significant quantities of SWNT.

Various processes are used to produce SWNT including physical methods(e.g., electrical arc, laser ablation) and chemical methods (e.g.,pyrolysis, chemical vapor deposition). Bench production yield from thesemethods is low and expensive. In addition, the product is not homogenousand contains tubes with broad diameter distributions and varioushelicity and thereby various electrical and mechanical properties, whichlimit their broader applications. Accordingly, there is a need in theart for methods for controllably producing SWNT with narrowdistributions of structural helices, and high yields.

BRIEF SUMMARY

It has been found that single-walled carbon nanotubes may be producedusing a chemical vapor deposition (CVD) method in which liquid catalyticdroplets are contacted with a carbon source in the reactor. Theresulting single walled carbon nanotube is formed at the surface of theliquid catalyst droplets. Use of liquid catalyst droplets provides asmooth, spherical shape that is not disturbed by various facets andsurface defects inherent in solid catalysts and supports, and thus, itprovides a more uniform surface for nanotube growth that produces a morehomogeneous nanotube product, depending only on the diameter of thedroplet.

Accordingly, in one aspect, the present disclosure is directed to amethod for producing a single-walled carbon nanotube in a chemical vapordeposition (CVD) reactor. The method includes contacting liquid catalystdroplets and a carbon source in the reactor; and forming a single walledcarbon nanotube at the surface of the liquid catalyst droplets.

In another aspect, the present disclosure is directed to a method forproducing a single-walled carbon nanotube in a chemical vapor deposition(CVD) reactor. The method includes introducing colloidal solid catalystparticles into a reactor at a decomposition temperature above themelting point of the catalyst particles to form liquid catalystdroplets; contacting the liquid catalyst droplets and a carbon source inthe reactor at a synthesis temperature above the decompositiontemperature; and forming a single walled carbon nanotube at the surfaceof the liquid catalyst droplets.

In yet another aspect, the present disclosure is directed to a method ofproducing a single-walled carbon nanotube. The method includes injectinga catalyst metalorganic precursor (e.g., metallocene) into a chemicalvapor deposition (CVD) reactor at a decomposition temperature above themelting point of the catalyst to remove the organic material and toforming liquid catalyst droplets; contacting the liquid catalystdroplets and a carbon source in the reactor at a synthesis temperatureabove the decomposition temperature; and growing the single-walledcarbon nanotube at the surface of the liquid catalyst droplets.

In yet another aspect, the present disclosure is directed to a method ofproducing a single-walled carbon nanotube. The method includes injectionof vapor of a powdered catalyst metalorganic precursor (e.g.,metallocene) into a carrier gas in a chemical vapor deposition (CVD)reactor at a decomposition temperature above the melting point of thecatalyst to remove the organic material and to form liquid catalystdroplets; transporting the liquid catalyst droplets from thedecomposition zone of the reactor to a growing zone of the reactor withthe carrier gas; contacting the liquid catalyst droplets and a carbonsource in the reactor at a synthesis temperature above the decompositiontemperature; and growing the single-walled carbon nanotube at thesurface of the liquid catalyst droplets.

The features, functions, and advantages described herein may be achievedindependently in various embodiments of the present disclosure or may becombined in yet other embodiments, further details of which may be seenwith reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example implementation of a vertical CVD reactorutilized in the methods described herein.

FIG. 2 shows an example implementation of a horizontal CVD reactorutilized in the methods described herein.

FIG. 3A shows a solid catalyst particle with facets or surface defects,and FIG. 3B shows a liquid catalyst droplet of the present method.

FIGS. 4A and 4B show example implementations of vertical CVD reactorsutilized in the methods described herein.

FIG. 5 shows a flow chart representation of an exemplary method ofproducing SWNT in a CVD reactor.

FIG. 6 shows a flow chart representation of an exemplary method ofproducing SWNT in a CVD reactor using colloidal solid catalyst particlesas a catalyst precursor.

FIG. 7 shows a flow chart representation of an exemplary method ofproducing SWNT in a CVD reactor using a catalyst metalorganic precursor.

FIG. 8 shows a TEM image of hcp Ga nanoparticles suitable for use as acatalyst using the methods described herein.

FIG. 9 shows a TEM image of In nanoparticles suitable for use as acatalyst using the methods described herein.

FIG. 10 shows a TEM image of nanotubes formed using gallium (III)acetylacetonate in ethanol as a catalyst precursor at a growthtemperature of about 900° C. using the methods described herein.

FIG. 11 shows a TEM image of nanotubes formed using gallium (III)acetylacetonate in ethanol as a catalyst precursor at a growthtemperature of about 925° C. using the methods described herein.

FIG. 12 shows Ramen spectra of nanotubes formed using the methodsdescribed herein.

FIG. 13 shows Ramen spectra of nanotubes formed using the methodsdescribed herein, and showing the radial breathing modes.

Although specific features of various implementations may be shown insome drawings and not in others, this is for convenience only. Anyfeature of any drawing may be referenced and/or claimed in combinationwith any feature of any other drawing.

DETAILED DESCRIPTION

The subject matter described herein relates generally to methods forproducing a single-walled carbon nanotube by a chemical vapor deposition(CVD) method. Generally, the methods include contacting liquid catalystdroplets and a carbon source in the reactor, and forming a single walledcarbon nanotube at the surface of the liquid catalyst droplets. Thefollowing detailed description illustrates implementations of thesubject matter described in this application by way of example and notby way of limitation.

Carbon nanotubes are allotropes of carbon, typically with asubstantially cylindrical nanostructure. Carbon nanotubes arecategorized as single-walled nanotubes (SWNT) and multi-walled nanotubes(MWNT). SWNT have a single layer of carbon comprising its microstructurewhile MWNT are comprised of several layers. While described herein withrespect to SWNT, it should be understood that the methods of the presentdisclosure are applicable to the formation of both SWNT and MWNT.

Catalysts used in the methods of the present disclosure are particularlysuitable to initiate and increase the rate of chemical reactions whichproduce SWNT. More specifically, the catalysts of the present disclosureinteract with a carbon source, further described below, to form SWNT.The catalysts serve as the formation surface for SWNT. Any catalysts andcatalyst mixtures having a melting point lower than the SWNT synthesistemperature may be used in the present disclosure. More specifically,the catalysts described herein may include materials including iron,nickel, cobalt, copper, chromium, indium, gallium, platinum, manganese,cerium, europium, ytterbium, silver, gold, zinc, cadmium, and lanthanum,any other catalysts known in the art, and compounds and combinationsthereof. In particularly suitable embodiments, the catalysts includeindium, gallium, and combinations thereof.

The catalysts used in the methods of the present disclosure may beprepared in many different forms. Non-limiting examples include acatalyst precursor material that is formed as a solid catalyst particle,a catalyst precursor material that is formed as a solid that isdispersed in a liquid, or a catalyst precursor material that isdissolved in a solvent. In an illustrative example, the catalystprecursor material is formed in a colloidal solid catalyst particle. Thecolloidal solid catalyst particle may be dispersed in a liquid. In anon-limiting example, the liquid may be an organic solution. In anon-limiting example, the catalyst precursor material is a colloidalsolid catalyst particle, and the liquid has a decomposition temperaturelower than the vaporization temperature of the catalyst.

In another non-limiting example, the catalyst precursor materials may bea catalyst metalorganic precursor (e.g., metallocene). Metalloceneprecursors of the present disclosure typically include catalyst metalsbonded to organic material (e.g., cyclopentadienyl anions). Non-limitingexamples of suitable catalyst metalorganic precursors include: galliumacetylacetonate, indium acetylacetonate, ruthenium acetylacetonate,gallium acetate, indium acetate, ruthenium acetate, gallium nitrate,indium nitrate, ruthenium nitrate, gallium sulfate, indium sulfate,ruthenium sulfate, gallium chloride, indium chloride, rutheniumchloride, and any combination thereof. It is to be understood that themetallocene precursor may also be provided as a solid powder, as a soliddispersed in a liquid, or dissolved in a solvent.

Catalysts used in the methods of the present disclosure, described morefully above, are configured to form liquid catalyst droplets thatprovide surfaces for the growth of SWNT during catalytic decompositionof a carbon source. The carbon source used in the methods of the presentdisclosure include elemental carbon and any carbon containing sourcecapable of providing elemental carbon for the formation of SWNT. Ingeneral, any carbon containing gas that does not pyrolize attemperatures up to 500° C. to 1000° C. can be used. Non-limitingexamples include carbon monoxide, aliphatic hydrocarbons, both saturatedand unsaturated, such as methane, ethane, propane, butane, pentane,hexane, acetylene, ethylene, and propylene; oxygenated hydrocarbons suchas acetone, methanol, and ethanol; aromatic hydrocarbons such asbenzene, toluene, and naphthalene; and mixtures of the above, forexample carbon monoxide and methane. The carbon source may optionally bemixed with a diluent gas such as hydrogen, helium, argon, neon, kryptonand xenon or a mixture thereof.

The catalyst droplets in the described methods provides for adecomposition reaction of the carbon source to elemental carbon with alower activation energy. Still in another example, the catalyst dropletsprovide for a formation reaction of elemental carbon to SWNT with alower activation energy. As shown in FIG. 3A, solid catalytic material302 includes facets or defects 304 on the surface where the nanotube306A/306B grows during synthesis. Such surface variations result in aheterogeneous nanotube product, as evidenced by the variation in sizebetween nanotubes 306A and 306B. In contrast, a support free liquidcatalyst droplet 308 as used in the methods of the present disclosureand as shown in FIG. 3B provides a smooth, spherical shape 310 that isnot disturbed by various facets and surface defects inherent in solidcatalytic material and supports. Therefore, it provides a more uniformsurface for nanotube growth that produces a more homogeneous nanotubeproduct, as evidenced by the uniform sizes of nanotubes 306C and 306Dformed on the free liquid catalyst droplet 308.

In some embodiments of the present disclosure, the reactants used in thechemical process of forming SWNT include a carrier gas In methods of thepresent disclosure, the carrier gas is typically a gas used as a masstransport mechanism but may also be used to dilute the reactants or slowthe reaction rate. The carrier gas used in methods of the presentdisclosure may include one or more inert gases (e.g., nitrogen, helium,neon, argon, etc.) or any other gas that may be suitable for improvingthe formation of SWNT as known in the art. Non-limiting examples ofother suitable gases include: hydrogen, carbon dioxide, ammonia, and anycombination thereof.

In some embodiments of the present disclosure, the carrier gas maytransport the reactants through the various zones of the reactor,promote mixing of the liquid catalyst droplets and carbon source,inhibit the introduction of unwanted gaseous reactants including, butnot limited, to air or oxygen, and/or maintain the reactants in asuitable position within the zones of the reactor. By way ofnon-limiting example, the carrier gas may offset the effect of gravityon the various particulate reactants within a vertically-orientedreactor, thereby maintaining the particulate reactants at a suitablevertical position within the reactor. Non-limiting examples ofparticulate reactants maintained in a suitable position within thereactor by the carrier gas include: catalyst particles, liquid catalystdroplets, and SWNT produced by the reactor.

In some embodiments of the present disclosure, the carrier gas may beinjected or inserted into the reactor at a flow rate ranging from about500 sccm (standard cubic cm/min.) to about 2000 sccm. In various otherembodiments of the present disclosure, the carrier gas may be injectedor inserted into the reactor at a flow rate ranging from about 500 sccmto about 600 sccm, 550 sccm to about 650 sccm, 600 sccm to about 700sccm, 650 sccm to about 750 sccm, 700 sccm to about 800 sccm, 750 sccmto about 850 sccm, 800 sccm to about 900 sccm, 850 sccm to about 950sccm, 900 sccm to about 1000 sccm, 950 sccm to about 1050 sccm, 1000sccm to about 1200 sccm, 1100 sccm to about 1300 sccm, 1200 sccm toabout 1400 sccm, 1300 sccm to about 1500 sccm, 1400 sccm to about 1600sccm, 1500 sccm to about 1700 sccm, 1600 sccm to about 1800 sccm, 1700sccm to about 1900 sccm, and from about 1800 sccm to about 2000 sccm.

The liquid catalyst droplets and carbon source are generally contactedto form the carbon nanotubes in any type of reactor known in thenanotube formation art. Generally, carbon nanotubes are formed by anumber of different chemical processes including pyrolysis and chemicalvapor deposition (CVD) in a number of different types of reactors. Suchreactors are suitable for methods of the present disclosure. Moreparticularly, reactors of the present disclosure may include a pluralityof zones including one or more of an injection zone, a decompositionzone, a size selection zone, a growing zone, a cooling zone, and acollection zone. It should be understood by one skilled in the art thatthe reactors used in the methods of the present disclosure may includeany combination of these zones in any suitable orientation withoutdeparting for the scope of the present disclosure. Reactors used in themethods of the present disclosure are configured both horizontally andvertically.

FIGS. 1 and 2 provide non-limiting examples of CVD reactors that can beused in the methods of the present disclosure.

FIG. 1 is a schematic illustration of an exemplary vertically-orientedCVD reactor 100 in one embodiment. The CVD reactor 100 may include aninjection zone 102 to introduce the catalyst material and carbon sourceto the CVD reactor 100, a decomposition zone 104 to partially orcompletely decompose one or more of the reagents within the CVD reactor100, a growing zone 106 to grow SWNT, a cooling zone 108 to cool thereactants and/or products in the CVD reactor 100, and a collection zone110 to collect products and unreacted reactants from the CVD reactor100.

As illustrated in FIG. 1, the injection zone 102 may be configured toinject or insert the catalyst material or catalyst precursor material124, and the carbon source 126 into the reactor 100. In particularlysuitable embodiments, the injection zone 102 includes one or more feedmechanisms (e.g., a syringe, pump, atomizer, nozzle, etc.), which arecapable of controlling a number of different variables with respect tothe catalyst or catalyst precursor 124, and carbon source 126 enteringthe reactor 100 including, but not limited to: volume, ratio, flow rate,and pressure. The injection zone 102 may also operate to increase thesurface area of the reactants as they enter the reactor and/or contactthe catalyst 124 and the carbon source 126. In one embodiment, theinjection zone may include an injector 112 to inject the catalyst orcatalyst precursor 124 into the injection zone 102 for subsequenttransport to other zones of the reactor 100 including, but not limitedto, the decomposition zone 104.

The decomposition zone 104 of the reactor 100 used in the methods of thepresent disclosure may be configured to partially or completelydecompose one or more of the catalyst precursor material 124, carbonsource 126 and any liquids entering or exiting the reactor 100. Forexample, the decomposition zone 104 may be configured to evaporate ordecompose a liquid or solvent in which the catalyst precursor 124 may bedispersed or otherwise dissolved, transform the catalyst precursor 124to liquid catalyst droplets, melt solid catalyst material 128 introducedto the decomposition zone 104 to form liquid catalyst droplets 130,maintain liquid catalyst droplets 130 introduced to the decompositionzone 104, or any combination thereof. The decomposition zone 104 may bemaintained at optimal temperature, pressure, and/or pH conditions tofacilitate such processes. The decomposition zone 104 may be maintainedat a temperature above the melting point of the solid catalyst material124 used in the methods, but below the vaporization temperature of theresulting liquid catalyst droplets 130. Accordingly, the temperature ofthe decomposition zone may be adjusted to accommodate the selectedcatalyst material 124 and carbon source 126. The decomposition zone 104may be heated with any type of heating mechanism without limitation. Inone non-limiting example, the decomposition zone 104 may include aplasma (not illustrated) to transform the catalyst precursor 124 tocatalyst particles 128.

In one embodiment, the decomposition zone 104 may be maintained at adecomposition temperature ranging from about 150° C. to about 400° C. Inanother embodiment, the decomposition zone 104 may be maintained at adecomposition temperature ranging from about 200° C. to about 300° C. Inother embodiments, the decomposition zone 104 may be maintained at adecomposition temperature ranging from about 150° C. to about 170° C.,from about 160° C. to about 180° C., from about 170° C. to about 190°C., from about 180° C. to about 200° C., from about 190° C. to about210° C., from about 200° C. to about 220° C., from about 210° C. toabout 230° C., from about 220° C. to about 240° C., from about 230° C.to about 250° C., from about 240° C. to about 260° C., from about 250°C. to about 270° C., from about 260° C. to about 280° C., from about270° C. to about 290° C., from about 280° C. to about 300° C., fromabout 290° C. to about 310° C., from about 300° C. to about 320° C.,from about 310° C. to about 330° C., from about 320° C. to about 340°C., from about 330° C. to about 350° C., from about 340° C. to about360° C., from about 350° C. to about 370° C., from about 360° C. toabout 380° C., from about 370° C. to about 390° C., and from about 380°C. to about 400° C.

The decomposition zone 104 of the reactor 100 may also serve as the areafor contacting the liquid catalyst droplets 130 and the carbon source126. Therefore, the decomposition zone 104 may be maintained at adecomposition temperature selected to allow for the catalyticdecomposition of the carbon source 126 and subsequent growth of thesingle-walled carbon nanotubes (SWNT) 120 on the liquid catalystdroplets 130 in the growing zone 106.

The growing zone 106 of the reactor 100 used in the methods of thepresent disclosure is typically configured to grow SWNT 120. Tofacilitate SWNT growth, the growing zone 106 may be maintained atoptimal temperature and/or pressure conditions. In one embodiment, thegrowing zone 106 may be maintained at a synthesis temperature rangingfrom about 500° C. to about 1300° C. In another embodiment, the growingzone 106 may be maintained at a synthesis temperature ranging from about800° C. to about 1200° C. In an additional embodiment, the growing zone106 may be maintained at a synthesis temperature ranging from about 900°C. to about 1050° C.

In other additional embodiments, the growing zone 106 may be maintainedat a synthesis temperature ranging from about 500° C. to about 600° C.,from about 550° C. to about 650° C., from about 600° C. to about 700°C., from about 650° C. to about 750° C., from about 700° C. to about800° C., from about 750° C. to about 850° C., from about 800° C. toabout 900° C., from about 850° C. to about 950° C., from about 900° C.to about 1000° C., from about 950° C. to about 1050° C., from about1000° C. to about 1100° C., from about 1050° C. to about 1150° C., fromabout 1100° C. to about 1200° C., from about 1150° C. to about 1250° C.,and from about 1200° C. to about 1300° C.

The cooling zone 108 of the reactor 100 used in the methods of thepresent disclosure is typically configured to cool the reactants and/orproducts in the reactor 100. In particularly suitable embodiments, thecooling zone 108 is maintained at a cooling temperature below thesolidification temperature of one or more reactants or products so as toinitiate solidification, freezing, or deposition.

The collection zone 110 of the reactor 100 used in the methods of thepresent disclosure is typically configured to collect the SWNT 120produced within the growth zone 106 as well as any unreacted reactants132 from the reactor 100. In particularly suitable embodiments, thecollection zone 110 is situated at an end of the reactor 100 oppositethe injection zone 102.

FIG. 2 is a schematic illustration of an exemplary horizontally-orientedCVD reactor 100A in one embodiment. The CVD reactor 100 may include aninjection zone 102 to introduce the carbon source 116 and a carrier gas202 to the CVD reactor 100, a decomposition zone 104 to partially orcompletely decompose one or more of the reagents within the CVD reactor100, a growing zone 106 to grow SWNT, a cooling zone 108 to cool theSWNT products, and a collection zone 110 to collect the SWNT productsand unreacted reactants from the CVD reactor 100.

The injection zone 102 of the reactor 100A may be configured to injector insert the carbon source 126 and a carrier gas 202 into the reactor100A. In particularly suitable embodiments, the injection zone 102includes one or more feed mechanisms (e.g., a syringe, pump, atomizer,nozzle, etc.), which are capable of controlling a number of differentvariables with respect to the carbon source 126 and the carrier gas 202entering the reactor 100A including, but not limited to: volume, ratio,flow rate, and pressure. As illustrated in FIG. 2, one feed mechanism204 may include an elongated conduit 208 to introduce the carbon source116 into one end of the growing zone 106 of the reactor 100A. In anotheraspect, a second feed mechanism 206 may be configured to introduce thecarrier gas 202 used to transport the reactants through the reactor 100Ainto the decomposition zone 104.

As illustrated in FIG. 2, the decomposition zone 104 may be configuredto receive a powdered catalyst metallocene precursor 210 in a carrier212. The decomposition zone 104 may be further configured to partiallyor completely decompose the powdered catalyst metallocene precursor 210and to form catalyst liquid droplets 130. The decomposition zone 104 maybe maintained at optimal temperature, pressure, and/or pH conditions tofacilitate such processes. The decomposition zone 104 may be maintainedat a temperature above the melting point of the solid catalyst material124 used in the methods, but below the vaporization temperature of theresulting liquid catalyst droplets 130. Accordingly, the temperature ofthe decomposition zone may be adjusted to accommodate the selectedcatalyst material 124 and carbon source 126.

In one embodiment, the decomposition zone 104 may be maintained at adecomposition temperature ranging from about 200° C. to about 300° C. Inother embodiments, the decomposition zone 104 may be maintained at adecomposition temperature ranging from about 200° C. to about 220° C.,from about 210° C. to about 230° C., from about 220° C. to about 240°C., from about 230° C. to about 250° C., from about 240° C. to about260° C., from about 250° C. to about 270° C., from about 260° C. toabout 280° C., from about 270° C. to about 290° C., and from about 280°C. to about 300° C.

The growing zone 106 of the reactor 100A used in the methods of thepresent disclosure is typically configured to grow SWNT 120. Tofacilitate SWNT growth, the growing zone 106 may be maintained at anoptimal temperature and/or pressure conditions. Any form of heating maybe provided to maintain the growing zone 106 at the desired synthesistemperature. In one embodiment, the growing zone 106 may be maintainedat a synthesis temperature ranging from about 500° C. to about 1300° C.In another embodiment, the growing zone 106 may be maintained at asynthesis temperature ranging from about 800° C. to about 1200° C. In anadditional embodiment, the growing zone 106 may be maintained at asynthesis temperature ranging from about 900° C. to about 1050° C.

In other additional embodiments, the growing zone 106 may be maintainedat a synthesis temperature ranging from about 500° C. to about 600° C.,from about 550° C. to about 650° C., from about 600° C. to about 700°C., from about 650° C. to about 750° C., from about 700° C. to about800° C., from about 750° C. to about 850° C., from about 800° C. toabout 900° C., from about 850° C. to about 950° C., from about 900° C.to about 1000° C., from about 950° C. to about 1050° C., from about1000° C. to about 1100° C., from about 1050° C. to about 1150° C., fromabout 1100° C. to about 1200° C., from about 1150° C. to about 1250° C.,and from about 1200° C. to about 1300° C.

The cooling zone 108 of the reactor 100A used in the methods of thepresent disclosure is typically configured to cool the reactants and/orproducts in the reactor 100A. In particularly suitable embodiments, thecooling zone 108 is maintained at a cooling temperature below thesolidification temperature of one or more reactants or products so as toinitiate solidification, freezing, or deposition.

The collection zone 110 of the reactor 100A used in the methods of thepresent disclosure is typically configured to collect the SWNT 120produced within the growth zone 106 as well as any unreacted reactants132 from the reactor 100A. In particularly suitable embodiments, thecollection zone 110 is situated at an end of the reactor 100A oppositethe injection zone 102.

In various other embodiments, the CVD reactor 100 may further include asize selection zone 402, as illustrated in FIGS. 4A and 4B. The optionalsize selection zone 402 is configured to separate out a catalystmaterial or catalyst precursor material 128 with a desired particle sizedistribution. Accordingly, the size selection zone 402 can be providedat any point in the method prior to the growth of nanotubes on theliquid catalyst droplets 130. In a non-limiting example, the sizeselection zone or step can be performed by using a cylindricaldifferential mobility analyzer (DMA) and an ultrafine condensationparticle counter. For instance, the particle size and distribution couldbe determined by on-line aerosol size classification using the DMA andthe ultrafine condensation particle counter as described in Lenggoro etal., “Sizing of Colloidal Nanoparticles by Electrospray and DifferentialMobility Analyzer Methods,” Langmuir, 2002, 18, 4584-4591, which ishereby incorporated by reference to the extent it is consistentherewith. The DMA allows for the isolation of catalyst material orcatalyst precursor material particles that fall within a desired rangeof electrical mobility from a steady stream of charged particlessuspended in a gas. The narrow range of electrical mobilities in theaerosol that is classified by the DMA directly translates to a narrowrange of particle size. Such controlled particle size distributionprovides for a more homogenous growth environment, and the resultingnanotube product.

Without being limited to any particular theory, colloidal chemistryallows for the production of catalyst precursor materials having anarrow particle size distribution, thereby resulting in liquid catalystdroplets having a narrow particle size distribution. Therefore, the useof a size selection step for colloidal catalyst material may beoptional. In a non-limiting example, the size selection step may beperformed before introduction of the colloidal catalyst particles intothe reactor.

However, colloidal catalyst precursors may be expensive to produce.Accordingly, the size selection step allows the use of less expensivecatalyst material or catalyst material precursors production methodsthat would otherwise produce a broad particle size distribution for theliquid catalyst droplets and catalyst material precursors, such ascatalyst metalorganic precursors (e.g., metallocene). As shown in FIGS.4A and 4B, a catalyst material precursor 124, such as a catalystmetallocene precursor 204, is introduced into the reactor 100. Thecatalyst precursor 124 may be in the form of a solid powder, a soliddispersed in a liquid, or the catalyst material may be dissolved in asolvent 404. In the event the catalyst precursor 124 is dispersed in aliquid or dissolved in a solvent 404, the liquid or solvent 404 isevaporated when introduced into the injection zone 102 and/ordecomposition zone 104 of the reactor 100. In addition, if the catalystmaterial precursor 124 is provided in the form of a catalyst metalloceneprecursor 204, the catalyst metallocene precursor 204 may be pyrolizedto form catalyst particles 128. In some embodiments, the evaporatedsolvent 404 may be separated from the catalyst particles 128 and ejectedfrom the reactor 100, as illustrated in FIG. 4A and FIG. 4B. In otherembodiments, the solvent may be retained along with the catalystparticles 128. By way of non-limiting example, the evaporated solvent404 may be a carbon-containing solvent such as ethanol that may beevaporated and used as a carbon source 126 in the growing zone 106.

As shown in FIGS. 4A and 4B, the catalyst particles 128 enter the sizeselection zone 402 so that catalyst particles 128 within the desiredparticle size distribution are allowed to enter the growing zone.Although FIGS. 4A and 4B illustrate catalyst particles 128 entering thesize selection zone 402, the catalyst may alternatively be in the formof liquid catalyst droplets 130 when entering and exiting the sizeselection zone (not illustrated). The growing zone 106 is maintained ata synthesis temperature that is above the melting point of the catalystparticles 128 so that the catalyst is maintained in the form of liquidcatalyst droplets 130. The carbon source 126 is introduced in thegrowing zone 106 so that nanotubes (not illustrated) are formed on thesurface of the liquid catalyst droplets 130.

As shown in FIG. 4A, all of the steps of the method may occur in asingle reactor 100, or they may be performed in separate reactor stages406/408 as shown in FIG. 4B. Therefore, the catalyst particles 128 maybe formed at a location separate from the size selection device 402 andthe growing zone 106. Alternatively, the catalyst particles 128 may beformed and undergo the size selection step at one location, andintroduced to the growing zone 106 at another location.

FIG. 5 is a flow chart of one embodiment of a method 500 of producingsingle-walled carbon nanotubes (SWNT) in a CVD reactor. Any embodimentof the CVD reactor 100/100A illustrated in FIGS. 1, 2, 4A, and 4B may beused to effectuate this method 500. As illustrated in FIG. 5, the method500 may include contacting liquid catalyst droplets and a carbon sourceat a synthesis temperature at step 502. Generally, the method forproducing SWNT in a CVD reactor of the present disclosure includescontacting the liquid catalyst droplets described herein above and acarbon source described herein above within the growing zone 106 of thereactor 100/100A described herein above and illustrated in FIGS. 1 and2. The synthesis temperature may range from about 500° C. to about 1300°C. or may be selected from one of the synthesis temperature rangesprovided herein above. As described herein previously, the synthesistemperature may be selected based on any one of at least several factorsincluding but not limited to: the composition of the liquid catalystdrops and the composition of the carbon source.

Referring again to FIG. 5, the method may further include forming theSWNT at the surface of the liquid catalyst droplets at step 504. Asdescribed herein above, the SWNT are formed as a result of a catalyticdecomposition of the carbon source to elemental carbon at the surface ofthe liquid catalyst droplets. The SWNT formed at step 504 may becollected for subsequent use (step not shown).

FIG. 6 is a flow chart of another embodiment of a method 600 ofproducing single-walled carbon nanotubes (SWNT) in a CVD reactor. Themethod 600 includes introducing colloidal solid catalyst particles intothe reactor at a decomposition temperature to form liquid catalystdroplets at step 602. By way of non-limiting example, step 602 may beconducted by injecting colloidal solid catalyst particles into aninjection zone 102 at one end of a reactor 100 as described herein aboveand as illustrated in FIG. 1. The colloidal solid catalyst particles maymove into a decomposition zone 104 of the reactor 100 as illustrated inFIG. 1 by gravity alone or by any other method of moving particleswithin a reactor as known in the art. The decomposition zone 104 ismaintained at the decomposition temperature. The decompositiontemperature may be any decomposition temperature provided herein above,including but not limited to a decomposition temperature ranging fromabout 200° C. to about 300° C.

The liquid catalyst droplets may be formed at step 602 by melting thecolloidal solid catalyst particles as they move through a decompositionzone 104 as illustrated in FIG. 1. Depending on the form in which thecolloidal solid catalyst particles are provided, the colloidal solidcatalyst particles may be subjected to additional processes. If thecolloidal solid catalyst particles are provided as a suspension within asolution, the solution surrounding the colloidal solid catalystparticles may be thermally removed at step 604 as illustrated in FIG. 6.In some embodiments, the solution surrounding the colloidal solidcatalyst particles may be evaporated or thermally decomposed in thedecomposition zone 104 of the reactor 100 as illustrated in FIG. 1. In anon-limiting example, the thermal decomposition of the solutionsurrounding the colloidal solid catalyst particles may occur before themelted catalyst (i.e., liquid catalyst droplets) contact the carbonsource.

In some embodiments, the liquid catalyst droplets may undergo sizeselection at step 606. Any known method may be used to subject theliquid catalyst droplets to size selection at step 606 including, butnot limited to size selection within a size selection zone 402 of areactor 100 as illustrated in FIGS. 4A and 4B. By way of non-limitingexample, the liquid catalyst droplets may be selected for size using acylindrical differential mobility analyzer as described herein above. Inan embodiment, the catalyst may undergo size selection before contactingthe carbon source to promote homogeneous catalyst particle or dropletsize and uniform SWNT growth on the droplets.

Referring again to FIG. 6, the method 600 may further include contactingthe liquid catalyst droplets and a carbon source at a synthesistemperature at step 608 and forming the SWNT at the surface of theliquid catalyst droplets at step 610. Step 608 and step 610 of method600 correspond to steps 502 and 504 of method 500 as described hereinabove. According, steps 608 and 610 may be conducted as described hereinabove in connection with steps 502 and 504 of method 500, respectively.As illustrated in FIG. 1, the liquid catalyst droplets 130 move throughthe reactor 100 and contact a carbon source 126, typically in thegrowing zone 106. However, it should be understood that this reactioncan take place in one or more other zones of the reactor 100 asdescribed herein above without departing from the scope of the presentdisclosure. As described herein above, the SWNT are produced in thereactor by a decomposition reaction catalyzed along the surface of theliquid catalyst droplets.

The method 600 illustrated in FIG. 6 may further include cooling theliquid catalyst droplets to a solidification temperature at step 612. Asillustrated in FIG. 1, the liquid catalyst droplets with attached SWNT120 formed in the growing zone 106 may be transported into the coolingzone 108 of the reactor 100 using gravity or any other known means oftransporting particles within a reactor. Within the cooling zone 108,the liquid catalyst droplets may be solidified, and the solidifiedcatalyst with SWNT thereon may enter the collection zone 110 of thereactor, where the catalyst with SWNT is collected (step notillustrated). To facilitate the solidification of the liquid catalystdrops, the cooling zone 108 may be maintained at a cooling temperatureas described herein above. In one embodiment, the cooling temperaturemay be selected to be a temperature at or below the solidificationtemperature of the catalyst. In other embodiments, the coolingtemperature may be selected to be below the solidification temperatureof the catalyst. In these other embodiments, lower cooling temperaturesmay result in more rapid cooling rates of the liquid catalyst dropletswithin the cooling zone 108.

FIG. 7 is a flow chart of an additional embodiment of an exemplarymethod 700 of producing single-walled carbon nanotubes (SWNT) in a CVDreactor. The method 700 includes injecting a catalyst metalorganicprecursor into the reactor at a decomposition temperature at step 702.The catalyst metalorganic precursor may be provided in any formdescribed herein previously including, but not limited to: a solidpowder, a solid dispersed in a liquid, or dissolved in a solvent. In theevent the catalyst metalorganic precursor is dispersed in a liquid ordissolved in a solvent, the liquid or solvent may be evaporated whenintroduced into the injection zone 102 and/or decomposition zone 104 ofthe reactor 100 as described herein previously and illustrated in FIGS.4A and 4B. In some embodiments, the catalyst metalorganic precursor maybe provided in the form of a metallocene as described herein above.

Referring again to FIG. 7, the method may further include decomposingthe catalyst metalorganic precursor to form liquid catalyst droplets atstep 704. In various embodiments, the catalyst metalorganic precursormay be pyrolized to remove the organic material within the metalloceneto form catalyst particles as described herein previously. The resultingcatalyst particles may then be melted to form the liquid catalystdroplets. In this method 700, the decomposition temperature may beselected to be higher than the melting temperature of the catalyst, aswell as higher than the pyrolysis temperature of the organic materialswithin the catalyst metalorganic precursor. In various embodiments, thedecomposition temperature may range from about 200° C. to about 300° C.,or range within any of the other decomposition temperature rangesdescribed herein above.

In some embodiments, the liquid catalyst droplets may undergo sizeselection at step 706 using any known method including, but not limitedto size selection within a size selection zone 402 of a reactor 100 asillustrated in FIGS. 4A and 4B. By way of non-limiting example, theliquid catalyst droplets may be selected for size using a cylindricaldifferential mobility analyzer as described herein above. In anembodiment, the catalyst may undergo size selection before contactingthe carbon source to promote homogeneous catalyst particle or dropletsize and uniform SWNT growth on the droplets.

Referring again to FIG. 7, the method 700 may further include contactingthe liquid catalyst droplets and a carbon source at a synthesistemperature at step 708 and forming the SWNT at the surface of theliquid catalyst droplets at step 710. Step 708 and step 710 of method700 correspond to steps 502 and 504 of method 500 and may be conductedas described herein above in connection with steps 502 and 504 of method500, respectively. As illustrated in FIG. 1, the liquid catalystdroplets 130 move through the reactor 100 and contact a carbon source126, typically in the growing zone 106. However, it should be understoodthat this reaction can take place in one or more other zones of thereactor 100 as described herein above without departing from the scopeof the present disclosure. As described herein above, the SWNT areproduced in the reactor by a decomposition reaction catalyzed along thesurface of the liquid catalyst droplets.

The method 700 illustrated in FIG. 7 may further include cooling theliquid catalyst droplets to a solidification temperature at step 712. Inthis embodiment, step 712 of method 700 corresponds to step 612 ofmethod 600 and may be conducted as described herein above in connectionwith step 612 of method 600.

It should be understood by one skilled in the art that while the instantdisclosure discusses many of the steps of the method in one or morezones of the reactor, any of the steps can be performed in any one orcombination of the zones as commonly known in the CVD reactor artwithout departing from the scope of the present disclosure.

In another method (not illustrated) of the present disclosure, a SWNT isproduced in a vertical CVD reactor by injecting a catalyst metalloceneprecursor into the injection zone at one end of the reactor. Thecatalyst metallocene precursor enters the decomposition zone of thereactor, wherein the organic material within the metallocene isdecomposed. Typically, the decomposition zone has a temperature of fromabout 200-300° C. Catalyst moving through the decomposition zone iscontiguously melted into liquid catalyst droplets. Thereafter, thecatalyst droplets moving through the reactor contact a carbon source.SWNT are produced accordingly in the growing zone of the reactor alongthe surface of the catalyst droplets. The catalyst droplets and SWNTmove into the cooling zone of the reactor, which solidifies the catalystdroplets. Solidified catalyst and SWNT enter the collection zone of thereactor.

In still another method of the present disclosure (not illustrated), aSWNT may be produced in a horizontal CVD reactor 100A by placingpowdered catalyst metallocene precursor 210 into a carrier 212 asillustrated in FIG. 2. The carrier 212 is then placed in thedecomposition zone 104 of the reactor 100A, wherein the organic materialwithin the metallocene is decomposed. In a non-limiting example, thedecomposition zone 104 is maintained at a decomposition temperatureranging from about 200° C. to about 300° C. The catalyst metalloceneprecursor may be contiguously melted or evaporated. A carrier gas,including but not limited to the gases described herein above,transports the catalyst particles 130 to a growing zone 106 in thereactor 100A maintained at a synthesis temperature higher than themelting point of the catalyst. The resulting liquid catalyst dropletscontact the carbon source within the growing zone 106, and SWNT areproduced accordingly along the surface of the liquid catalyst droplets.The liquid catalyst droplets and SWNT enter the cooling zone 108 of thereactor 100A, which solidifies the catalyst droplets. Solidifiedcatalyst and SWNT enter the collection zone 110 of the reactor 100A.

Although described herein with respect to vertical and horizontalreactors configured perpendicular to each other, it is to be understoodthat the reactors are not limited to such configurations and that theycan be oriented at any angle with respect to horizontal and/or vertical.In addition, any form of catalyst or catalyst precursor material may beused in the reactors, as the reactor configurations are not limited tothe use of only solids, solids dispersed in liquids, or liquids.

It is also to be understood that the methods disclosed herein may beperformed in a continuous manner characterized by the continuousintroduction of the catalyst and the carbon source to the growing zoneto continuously grow carbon nanotubes. Accordingly, a greater volume ofcarbon nanotubes may be produced as compared to conventional batchmethods.

Methods of producing SWNT in a reactor are described herein above indetail. The methods are not limited to the specific embodimentsdescribed herein, but rather, components of systems and/or steps of themethod may be utilized independently and separately from othercomponents and/or steps described herein. Each method step and eachcomponent may also be used in combination with other method steps and/orcomponents. Although specific features of various embodiments may beshown in some drawings and not in others, this is for convenience only.Any feature of a drawing may be referenced and/or claimed in combinationwith any feature of any other drawing.

EXAMPLES Example 1 Synthesis of Ru Nanoparticles

To demonstrate a method of forming Ru nanoparticles suitable for use asa catalyst precursor in the methods described herein above, thefollowing experiment was conducted.

0.02 g of RuCl₃·xH₂O was dissolved in 25 mL of ethylene glycol. N₂ gaswas bubbled through the precursor solution vigorously while maintainingthe solution at a temperature of about 50° C. to remove air and moisturefrom the solution. After about ten minutes, the flow rate of the N₂ gaswas decreased and the temperature of the precursor solution wasincreased to 105° C. for 7 min. At this temperature, 0.10 g of sodiumacetate dissolved in 5 mL ethylene glycol was injected quickly intoprecursor solution, accompanied by a change in color of the precursorsolution to black. The temperature of the precursor solution was furtherincreased to 155° C. and subsequently 187° C. for an additional 1.5 hr.

The precursor solution was cooled, resulting in the precipitation of Runanoparticles from the precursor solution. The Ru nanoparticles wereseparated by centrifugation and washed two times with ethanol. Half ofthe resulting precipitate of Ru nanoparticles was dispersed in 0.15 g ofoleic acid and 0.1 g of oleylamine for hexagonal close-packed (hcp) Runanoparticles. This solution was sonicated for 30-60 min, stirred for 30min, and again sonicated for 30 min. The precipitate of this solutionwas isolated by centrifugation and washed two times with ethanol.

FIG. 8 is a TEM image of the hcp Ru nanoparticles formed as describedabove. The particle size of the hcp Ru nanoparticles was about 2 nm toabout 2.5 nm with high dispersity, high purity, and narrow sizedistribution.

The results of this experiment demonstrated a method of forming Runanoparticles suitable for use as a catalyst precursor in the methodsdescribed herein above.

Example 2 Synthesis of In Nanoparticles

To demonstrate a method of forming In nanoparticles suitable for use asa catalyst precursor in the methods described herein above, thefollowing experiment was conducted.

0.17 g of InCl₃ was dissolved in 5 mL of TOP (trioctylphosphine) and 10mL of THF (tetrahydrofuran) at room temperature. Once the indiumchloride had completely dissolved, 4 mL of superhydride solution wasinjected into the precursor solution. Within a few minutes, largeagglomerates formed within the solution. The solution was exposed to airand stirred for an additional 2-4 hours. The In nanoparticles wereseparated by centrifugation and washed two times with ethanol.

FIG. 9 is a TEM image of the resulting In nanoparticles formed asdescribed above. The particle size of the In nanoparticles was about 2nm with high dispersity, high purity, and narrow size distribution.

The results of this experiment demonstrated a method of forming Innanoparticles suitable for use as a catalyst precursor in the methodsdescribed herein above.

Example 3 Production of SWNT Using Liquid Catalyst Droplets

To demonstrate the method of producing single-walled carbon nanotubes(SWNT) using the methods described herein above, the followingexperiments were conducted.

A suspension of 0.4 wt % of gallium (III) acetylacetonate (Ga(acac)₃) inethanol was introduced into a vertical CVD reactor similar to thereactor illustrated in FIG. 1 at a liquid injection rate of about 6ml/hr. In addition, argon was introduced into the reactor at a rate ofabout 450 sccm and hydrogen was introduced at a rate of 75 sccm ascarrier gases. The acetylacetonate was pyrolized from the Ga(acac)₃ andthe remaining gallium was melted to form liquid gallium catalystdroplets. The liquid gallium droplets were contacted with the ethanolcarbon source for about 15 minutes at a synthesis temperature of about900° C. to form the SWNT. The liquid gallium droplets with attached SWNTwere cooled and collected for subsequent analysis. This experiment wasrepeated at a synthesis temperature of about 925° C.

FIG. 10 is a TEM image of the SWNT formed using the method describedabove at a synthesis temperature of about 900° C., and FIG. 11 is a TEMimage of the SWNT formed using the method described above at a synthesistemperature of about 925° C. Both TEM images indicate the presence ofnanotubes in the samples. FIG. 12 is a graph summarizing typical Ramanspectra obtained from samples of the SWNT, and FIG. 13 is a zoomed-ingraph of Raman spectra obtained from samples of SWNT. As illustrated inFIG. 13, Raman spectra are characterized by radial breathing modesindicative of SWNT.

The results of these experiments demonstrated that SWNT may be producedusing the methods described herein above.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art.

What is claimed is:
 1. A method for producing a single-walled carbonnanotube in a chemical vapor deposition (CVD) reactor comprising:contacting liquid catalyst droplets and a carbon source in the reactor;and forming a single walled carbon nanotube at the surface of the liquidcatalyst droplets.
 2. A method for producing a single-walled carbonnanotube in a chemical vapor deposition (CVD) reactor comprising:introducing colloidal solid catalyst particles into the reactor at adecomposition temperature above the melting point of the catalystparticles to form liquid catalyst droplets; contacting the liquidcatalyst droplets and a carbon source in the reactor at a synthesistemperature above the decomposition temperature; and forming a singlewalled carbon nanotube at the surface of the liquid catalyst droplets.3. The method in accordance with claim 2, further comprising thermallyremoving the solution surrounding the colloidal solid catalystparticles.
 4. The method in accordance with claim 2, further comprisingremoving the liquid catalyst droplets larger than a determined particlesize.
 5. The method in accordance with claim 2, further comprisingcooling the liquid catalyst droplets to a solidification temperature. 6.The method in accordance with claim 2, wherein the catalyst particlescomprise a material selected from the group consisting of iron, nickel,cobalt, copper, chromium, indium, gallium, platinum, manganese, cerium,europium, ytterbium, silver, gold, zinc, cadmium, lanthanum, andcombinations thereof.
 7. The method in accordance with claim 2, whereinthe carbon source is a material selected from the group consisting ofcarbon monoxide, ethanol, aliphatic hydrocarbons, oxygenatedhydrocarbons, aromatic hydrocarbons, and mixtures thereof.
 8. The methodin accordance with claim 2, wherein the reactor includes a vertical orhorizontal configuration.
 9. The method in accordance with claim 2,wherein the method continuously produces single-walled carbon nanotubesin the chemical vapor deposition (CVD) reactor.
 10. A method ofproducing a single-walled carbon nanotube comprising: injecting acatalyst metalorganic precursor comprising a catalyst into a chemicalvapor deposition (CVD) reactor at a decomposition temperature above themelting point of the catalyst to remove the organic material and to formliquid catalyst droplets; contacting the liquid catalyst droplets and acarbon source in the reactor at a synthesis temperature above thedecomposition temperature; and growing the single-walled carbon nanotubeat the surface of the liquid catalyst droplets.
 11. The method inaccordance with claim 10, further comprising removing the liquidcatalyst droplets larger than a determined particle size.
 12. The methodin accordance with claim 10, further comprising cooling the liquidcatalyst droplets in a cooling zone to a solidification temperature. 13.The method in accordance with claim 10, wherein the catalyst is amaterial selected from the group consisting of iron, nickel, cobalt,copper, chromium, indium, gallium, platinum, manganese, cerium,europium, ytterbium, silver, gold, zinc, cadmium, lanthanum, andcombinations thereof.
 14. The method in accordance with claim 10,wherein the carbon source is a material selected from the groupconsisting of carbon monoxide, ethanol, aliphatic hydrocarbons,oxygenated hydrocarbons, aromatic hydrocarbons, and mixtures thereof.15. The method in accordance with claim 10, wherein the decompositiontemperature ranges from about 150° C. to about 400° C.
 16. The method inaccordance with claim 10, wherein the synthesis temperature ranges fromabout 500° C. to about 1300° C.
 17. The method in accordance with claim10, wherein the liquid catalyst droplets and the carbon source arecontacted in a growing zone of the reactor.
 18. The method in accordancewith claim 10, wherein the method continuously produces single-walledcarbon nanotubes in the chemical vapor deposition (CVD) reactor.
 19. Amethod of producing a single-walled carbon nanotube comprising:injecting vapor of a powdered catalyst metalorganic precursor comprisinga catalyst into a carrier gas in a chemical vapor deposition (CVD)reactor at a decomposition temperature above the melting point of thecatalyst to remove the organic material and to form liquid catalystdroplets; transporting the liquid catalyst droplets from thedecomposition zone of the reactor to a growing zone of the reactor withthe carrier gas; contacting the liquid catalyst droplets and a carbonsource in the growing zone at a synthesis temperature above thedecomposition temperature; and growing the single-walled carbon nanotubeat the surface of the liquid catalyst droplets.
 20. The method inaccordance with claim 19, wherein the reactor is configuredhorizontally.
 21. The method in accordance with claim 19, wherein thecatalyst is a material selected from the group consisting of iron,nickel, cobalt, copper, chromium, indium, gallium, platinum, manganese,cerium, europium, ytterbium, silver, gold, zinc, cadmium, lanthanum, andcombinations thereof.
 22. The method in accordance with claim 19,wherein the carbon source is a material selected from the groupconsisting of carbon monoxide, ethanol, aliphatic hydrocarbons,oxygenated hydrocarbons, aromatic hydrocarbons, and mixtures thereof.23. The method in accordance with claim 19, wherein the carrier gas is amaterial selected from the group consisting of hydrogen, helium, argon,neon, krypton, xenon, and mixtures thereof.
 24. The method in accordancewith claim 19, wherein a plurality of single-walled carbon nanotubes aregrown on the surface of the liquid catalyst droplets.
 25. The method inaccordance with claim 19, wherein the decomposition temperature and thesynthesis temperature are below a vaporization temperature of the liquidcatalyst droplets.
 26. The method in accordance with claim 19, whereinthe method continuously produces single-walled carbon nanotubes in thechemical vapor deposition (CVD) reactor.